1. Field of the Invention
The present invention relates to a variable valve operation control apparatus, which controls variably valve opening/closing timing, valve opening period and/or valve lift of an intake valve and/or exhaust valve of an engine in accordance with engine operating conditions.
2. Related Art
It is known, as disclosed in JP-A-9-32519, to control variably a valve opening period and valve lift of an intake valve and/or exhaust valve of an engine by driving in an axial direction a camshaft having a cam profile, which varies in the axial direction.
It is also known, as disclosed in JP-A-9-151719, to control variably a phase of a second camshaft relative to a first camshaft in accordance with engine operating conditions, in a system where a driving force is transmitted from the first camshaft to the second camshaft. That is, a rotational phase of the second camshaft relative to the first camshaft is variably adjusted, so that the second camshaft adjusts an opening/closing timing of a valve associated with the second camshaft.
It is possible to combine the above two controls. That is, an axial driving mechanism for varying the valve opening period and the valve lift by driving the camshaft having the varying cam profile in the axial direction may be combined with a phase adjusting mechanism for adjusting the rotational phase of the second camshaft relative to the camshaft.
In this combined system, the phase adjusting mechanism is supported by the camshaft when the camshaft does not move in the axial direction, because the phase adjusting mechanism is normally supported by a member which does not move in the axial direction. The phase adjusting mechanism has a camshaft-side rotary body, which rotates with the camshaft. Therefore, in the case that the phase adjusting mechanism is assemble to the camshaft which does not move in the axial direction, it can be supported by simply fixing the camshaft-side rotary body to the camshaft by bolts or the like.
It is however required to support the phase adjusting mechanism rotatably not by the first camshaft but by a cylinder head of the engine, for instance, in the case that the phase adjusting mechanism is assembled to the first camshaft. Because the cylinder head is not rotatable, a rotatable member is required additionally to support the phase adjusting mechanism rotatably relative to the cylinder head, resulting in an increase in the number of component parts.
As the first camshaft is movable in the axial direction, a fluid passage formed in the first camshaft and a fluid passage formed in the phase adjusting mechanism must be held in communication with each other through a communication passage. Thus, for instance, the communication passage must be formed longitudinally, resulting in a complicated machining for the communication passage.
Further, gear teeth hitting sound is generated at a spline-engagement part which enables the axial movement of the camshaft and/or a gear-meshing part which transmits the driving force from the first camshaft to the second camshaft, because the second camshaft is subjected to positive and negative changes in torque applied thereto.